This invention relates to a glass breakage detector and more particularly to a device for detecting a breakage of a window to set off an appropriate alarm.
The prior art is replete with various devices which are employed in intrusion detection systems to provide an alarm upon the unauthorized entry of a person, such as a burglar. Certain of these devices are used to detect the breaking or cutting of window glass to gain entry to the secured premises. Probably the most familiar of such techniques employs a conductive metal foil which is secured about the periphery of the window or glass area and if the glass is broken, the foil will also break, thus activating an alarm. This technique requires great expense in installation, cannot be reused when a window is broken, is difficult to maintain and detracts from the overall appearance of the secured premises.
To circumvent this technique, the prior art discloses alternate types of sensors which employ resonant sensing elements which detect forces or vibration of the glass surface in a plane parallel to the plane of the glass. See U.S. Pat. No. 3,899,784 entitled GLASS BREAKAGE DETECTOR issued on Aug. 12, 1975. Other devices employ the piezoelectric effect as well as other devices which employ mechanical pendulums. Each device has its own particular advantage and disadvantages in regard to tolerance operation and adjustability. Patents which relate to the principles of glass breakage detection are U.S. Pat Nos. 3,899,784, 2,884,623, 3,706,090, 1,974,779, 3,441,925, 3,634,845, as well as others too numerous to mention.
In any event, it is apparent that a major factor in employing such devices is reliability as well as the cost of producing or manufacturing such a device.
It is therefore an object of the present invention to provide an improved detector apparatus for responding to a breakage of glass; which apparatus is reliable and simple to construct and employ.